Achieving effective atomization of liquids for injection into reciprocating or rotary internal combustion engines is an important aspect of the design and operation of spark-ignition, compression-ignition (diesel) or continuous combustion engines. Prior art methods include the use of very high pressures, use of very small orifices, and use of impingement plates or small cylindrical obstacles that break up a stream of liquid.
Achieving effective atomization of liquids for cooling, knock reduction, NOx reduction in reciprocating or rotary internal combustion engines is an important aspect of the design and operation and provides significant advantages with respect to increased fuel economy and lowered emissions.
Both liquid fuels and water are typically injected-into engines. Fuels can be diesel-type fuels, gasoline (petrol), alcohols, and mixtures thereof. Diesel-type fuels include JP-8, jet fuel, and kerosene. Alcohols include ethanol and methanol, which are commonly blended with gasoline. Water is also often injected into engines to provide an internal cooling effect, knock, NOx reduction and because of the large coefficient of expansion provided by liquid water converting to steam during combustion, particularly if there is net reduction in heat lost through external cooling and exhaust.
Modern engines typically use fuel injection to introduce fuel into the engine. Such fuel injection may be by port injection or direct injection. In port injection fuel injectors are located at some point in the intake train or intake manifold before the cylinder. In direct injection, an injector is in each cylinder.
Atomization of fuels and other liquids injected into cylinders is important. Optimally, any injected liquid is atomized prior to contact of the stream of injected liquid with any interior surface of the engine. If liquid contacts cylinder surfaces, it can wash away lubricants and pool, resulting in sub-optimal combustion. Pooled fuel during combustion causes carbon deposits, increased emissions, and reduced engine power. Alternatively, when water is injected, the impingement on non-lubricated internal surfaces, such as cylinder head and piston face, can provide some benefits.
The spray configuration in conventional fuel injectors or atomizers is typically cone-shaped, often with swirling, but this configuration is limited and can result in impaction of liquids on the piston and cylinder walls in direct injection systems. Particularly in high compression engines, the head space is very limited, making atomization in such engines more difficult without contact of streams of liquid on engine internal surfaces.
An approach to effective atomization is the use of high pressure liquid injection and small orifices, but high pressure systems are expensive and prone to failure, and small orifices are prone to clogging.
Also an approach to effective atomization is to use air shear with the liquid, where high pressure fast moving air is used to shear a liquid stream to achieve atomization. This approach has its own limitations in terms of breaking the liquid droplets. Additionally, its application in direct injection configuration is difficult, if not impossible, because of complexities involved with providing air or gas at high pressures.
Colliding jets are also well known in liquid fueled rocket engines, as a means of mixing the fuel and the oxidizer together. Injectors for internal combustion engines differ from prior art rocket engine nozzles in that rocket engine nozzles are not ‘start-hold-stop’ type metered devices, whereas injectors for internal combustion engines are designed to deliver, on command, a specific quantity of a liquid. This requires careful control over the flow rate over time, which is traditionally achieved via a solenoid, but can also be controlled via hydraulic pilot actuation, hydraulic amplification, piezo-electric stack, pneumatic means, or other methods. Moreover, colliding jets in rocket engines are primarily intended as a mixing method, in which two separate fluids (typically, a fuel and oxidizer) are injected to interact and react, rather than as a mechanism purely to break apart fluids into droplets or an atomized spray.
Conventional atomizers and injectors use high pressure to force liquids through a small orifice. The kinetic energy provided by application of pressure is therefore used almost entirely for acceleration of the fluid and any break up or atomization occurs due to air shear, resistance or drag. It is clear from observation as well as theory that the jet will travel substantial distance before the break up begins. In internal combustion engines with limited chamber dimensions, about 10 cm in most passenger cars, the ‘liquid length’ or the length of the jet before the break up is higher than the farthest point from the injector tip in a combustion chamber. This means the jets will impinge either the piston or the cylinder wall or both before the break up. A new mechanism is needed to achieve better breakup